Apparatus and methods for cooling semiconductor integrated circuit chip packages

ABSTRACT

Apparatus and methods are provided for integrating microchannel cooling modules within high-density electronic modules (e.g., chip packages, system-on-a-package modules, etc.,) comprising multiple high-performance IC chips. Electronic modules are designed such that high-performance (high power) IC chips are disposed in close proximity to the integrated cooling module (or cooling plate) for effective heat extraction. Moreover, electronic modules which comprise large surface area silicon carriers with multiple chips face mounted thereon are designed such that integrated silicon cooling modules are rigidly bonded to the back surfaces of such chips to increase the structural integrity of the silicon carriers.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. patent application Ser. No.10/987,985, filed on Nov. 12, 2004, which is fully incorporated hereinby reference.

GOVERNMENT RIGHTS

This invention was made with Government support under Contract No.H98230-04-C-0920 awarded by the Maryland Procurement Office. TheGovernment has certain rights in this invention.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to apparatus and methods forpackaging semiconductor IC (integrated circuit) chips with integratedcooling modules. More specifically, the present invention relates toapparatus and methods for integrating microchannel cooling moduleswithin high-density chip packages and system-on-a-package modulescomprising multiple high-performance IC chips.

BACKGROUND

In the design and manufacture of semiconductor IC chip packages andmodules (e.g., SCM (single chip modules), MCMs (multi-chip modules),etc.), it is imperative to implement mechanisms that can effectivelyremove heat generated by IC chips, such as microprocessors or otherhigh-performance chips, to ensure continued reliable operation of the ICchips. Effective heat removal becomes increasingly problematic as chipgeometries are scaled down and operating speeds are increased, whichresults in increased power density. Moreover, as chip packages orelectronic modules become more compact with multiple IC chips denselypacked together, the increased heat density generated by operation ofthe chips in such close proximity can adversely affect integratedcircuit components and cause physical damage to the package structuredue to differences in thermal expansion of the package components.Accordingly, there is a continuing need for improved devices and methodsfor effectively cooling high-density and/or high-performance IC chippackages and modules.

One method of dense packaging of high performance chips, known as“system on a package”, uses a silicon carrier with electrical throughvias as an additional intermediate package layer between the chips and aceramic first level package to provide high density and high performanceelectrical interconnects, such as described in U.S. Pat. No. 6,593,644,entitled “System on a Package Fabricated on a Semiconductor orDielectric Wafer with Wiring on One Face, Vias Extending Through theWafer, and External Connections on the Opposing Face,” which is commonlyassigned and fully incorporated herein by reference. Packagingstructures and method described in this patent provide a number ofsignificant advantages, but one critical factor that should beconsidered for practical implementations of package structures withsilicon carriers is the size and thickness of such silicon carriers. Fora silicon carrier to be useful, the carrier should be larger in sizethan the size of the chip or chip array to be mounted on the carrier.For example, the largest practical size for a high performance chip iscurrently about 20 mm×20 mm . Therefore, to mount a 2×2 array of suchchips, the silicon carrier would need to be over 40 mm×40 mm in size.

Another factor that is considered when using silicon carriers in packagestructures is the thickness of the silicon carrier. It is desirable tomake the silicon carrier substrate as thin as possible due thedifficulties associated with forming electrical through vias and fillingthe vias with a conductive material and minimizing the inductance of theelectrical interconnects. For example, if a silicon carrier is 0.2 mmthick and 40 mm wide, the width/thickness ratio is 200:1. As reported inthe literature, a practical silicon carrier thickness is primarilylimited by the ultimate aspect ratio of the through vias. In general,aspect ratio values much higher than about 10:1 are considered to bedifficult to manufacture and make highly reliable. By way of example,the consortium composed mainly of Japanese Electronics companies knownas the Association of Super-Advanced Electronic Technologies (ASET) hasworked intensively on silicon carrier through-via technology for thepast five years (see Takahashi, K. et al., “Current Status of Researchand Development of Three-dimensional Chip Stacking Technology”, Jpn. J.Appl. Phys. Vol. 40, (2001) pp. 3032-3037), and such work has culminatedin a reportedly robust process employing 10 um wide vias and a carrierthickness fixed at 50 um (see Takahashi, K. et al., “Process Integrationof 3D Chip Stack with Vertical Interconnection”, Proc. 54th Electron.Components and Technol. Conf. Las Vegas, Nev., June 2004, pp. 601-609).

Some of the practical difficulties which occur with a large area andthin silicon carrier include increased risk of fracturing the siliconcarrier during processing, bonding or assembly, as well as providing aneffective means for cooling the chips mounted on the silicon carrier. Itis difficult to use a conventional cooling means such as a thermal pastelayer and a heat sink attached to the back surface of the chips sincethe force used to hold the heat sink in place and the large force usedduring assembly to insure a thin and uniform thermal paste layer couldcrack the silicon carrier. Therefore, packaging structures and methodsthat provide increased stiffness of a silicon carrier while providing ahigh performance cooling solution are highly desirable.

SUMMARY OF THE INVENTION

Exemplary embodiments of the invention generally include apparatus andmethods for packaging semiconductor IC chips with integrated coolingmodules. More specifically, exemplary embodiments of the inventioninclude apparatus and methods for integrating microchannel coolingmodules within high-density electronic modules (e.g., chip packages,system-on-a-package modules, etc.,) comprising multiple high-performanceIC chips.

In general, electronic modules according to exemplary embodiments of theinvention are designed such that high-performance (high power) IC chipsare disposed in close proximity to an integrated cooling module (orcooling plate) for effective heat extraction. More specifically,exemplary embodiments of the invention include electronic modules whichcomprises an integrated cooling module and high-performance IC chipsbonded directly to the cooling module. For instance, in one exemplaryembodiment of the invention, the non-active surface of an IC chip can berigidly bonded to a microchannel cooler device using solder, silverfilled epoxy, or similar filled polymer.

In other exemplary embodiments of the invention, electronic modules aredesigned having a cooling module disposed between carrier substrateshaving a plurality of IC chips mounted on the carrier substrates. Insuch exemplary embodiments, high-performance IC chips are mounted insurface regions of the carrier substrates that are aligned with thecooling module. In other exemplary embodiments of the invention,conductive vias can be formed through the cooling module (e.g., inthermal microfins of a microchannel cooler) to provide electrical signalpaths across the cooling module between the carrier substrates and/orthe IC chips mounted on the carrier substrates.

In another exemplary embodiment of the invention, an electronic modulecomprises a first level carrier substrate and an intermediate carriersubstrate bonded to the first level carrier substrate, wherein theintermediate carrier substrate comprises a plurality of IC chipsflip-chip bonded thereto. A cooling device, such as a microchannelcooler, is thermally bonded to the non-active surfaces of each IC chipmounted on the intermediate carrier substrate using rigid bondingmaterial. The cooling device is formed of a material which is thermalexpansion matched to the material from which the intermediate substratecarrier is formed to reduce mechanical stresses caused by differences inthermal expansion. The microchannel cooling device provides cooling forthe chips and additionally increases the structural integrity of theelectronic assembly by rigidly bonding the microchannel cooler to theback surfaces of IC chips mounted on the intermediate carrier. Moreover,microchannel cooler is light weight and the bonding material can becompatible with a C4 reflow, such that the microchannel cooler could beassembled to the intermediate carrier package with the IC chips beforebonding the intermediate carrier package to the first level package.

Exemplary packaging methods and structures according to the inventionmay be used for building a compact computer system-on-a-packagecomprising multiple IC processor chips, IC memory chips, andcommunication chips and modules, which are densely packed together withan integrated cooling module. In such embodiments, the high-performanceIC processor chips are disposed in proximity to the integrated coolingmodule for efficient heat extraction.

These and other exemplary embodiments, aspects, features, and advantagesof the present invention will become apparent from the followingdetailed description of exemplary embodiments, which is to be read inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of an electronic module accordingto an exemplary embodiment of the invention.

FIG. 2 is a schematic perspective view of an electronic module accordingto another exemplary embodiment of the invention.

FIGS. 3A and 3B schematically illustrate a microchannel cooling devicewhich can be integrated within an electronic module according to anexemplary embodiment of the invention.

FIG. 4 schematically illustrates a microchannel cooling device which canbe integrated within an electronic module according to another exemplaryembodiment of the invention.

FIG. 5 schematically illustrates an electronic module according toanother exemplary embodiment of the invention.

FIG. 6 schematically illustrates an electronic module according toanother exemplary embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT

FIG. 1 is a schematic perspective view of an electronic module accordingto an exemplary embodiment of the invention. FIG. 1 schematicallyillustrates an exemplary embodiment of an electronic module (100)comprising an integrated cooling module (101) (e.g., microchannelcooler) with high-performance IC chips (102) and (103) bonded directlyto the cooling module (101). The cooling device (101) comprises amicrochannel cooling device having a plurality of coolant inlet/outlets(101 a) to enable coolant to flow in and out of the cooling device(101). In one exemplary embodiment, the electronic module (100)comprises a computer “system on a package” in a stacked chip structure,wherein the IC chips (102) and (103) are processor chips (e.g., CPUs,microprocessors, etc.). The back (non-active) surfaces of the ICprocessor chips (102) and (103) are thermally coupled to oppositesurfaces of the cooling device (101). Furthermore, an array of IC memorychips (104) and (105) are flip-chip bonded to the active surface of theIC processor chips (102) and (103), respectively. It is to be understoodthat depending on the application, the module (100) can have any numberand/or arrangement of IC memory chips bonded to the IC processor chips(102) and (103).

The electronic module (100) further comprises separate CIO(communication and input/output) modules (106) and (107) forcorresponding IC processor chips (102) and (103), respectively. The CIOmodule (106) is connected to the IC processor chip (102) via an array ofvertical pins, or solder columns, (108) mounted therebetween, and theCIO module (107) is connected to the IC processor chip (103) via anarray of vertical pins, or solder columns, (109) mounted therebetween.

In one exemplary embodiment of the invention, each vertical pin orsolder column may be formed of two separate solder bumps, wherein onesolder bump originates on an IC processor chip and another solder bumporiginates on a corresponding CIO module, thus giving an effective“double bump” standoff height. Moreover, the IC memory chips may bethinned considerably, e.g., to 100 microns thick, using standardbackside grind techniques, and the C4s used to join the IC memory chipsto the corresponding IC processor chips may be reduced in height, makingit possible to use more or less standard bumping techniques to assemblethe module (100).

The CIO modules (106) and (107) can be bonded thermally to thenon-active surfaces of the memory chips in IC memory chip arrays (104)and (105), respectively, if the CIO modules (106) and (107) need todissipate heat through the memory chips and the IC processor chips.Alternatively, if the power of the CIO modules (106) and (107) are low,enabling heat to be easily dissipated to the surroundings, the CIOmodules (106) and (107) do not have to be bonded to the respectivememory chips of chip arrays (104) and (105) to the memory chips.

The CIO modules (106) and (107) are constructed to include the requiredelectrical interconnects, bonding pads, integrated circuits/devices, I/Ocomponents, etc., that enable electrical connection/communication withother electronic components, devices, modules, power sources, etc. TheIC processor chips (102) and (103) can directly communicate via acommunication link provided by a flexible cable (110). Each end of thecable (110) is soldered to one of the IC processor chips (102) and (103)and disposed along the side of the module (100).

With the exemplary package structure of FIG. 1, the cooling device (101)is thermally coupled directly to IC processor chips (102) and (103) toprovide increased cooling capacity for the module (100). Indeed,high-performance IC chips such as computer processors typically havehigh average power densities and may contain “hot spot” regions withincreased (above-average) heat flux (power/unit area). Directlyconnecting the IC processor chips (102) and (103) to the cooling device(101) provides a low resistance heat conduction path and enablesincreased cooling. Further, the IC processor chips (102) and (103) areformed of a thermal conductive material (e.g., silicon) and act asthermal heat spreaders for extracting and conducting heat from thelow-power density chips (104) and (105) to the cooling module (101).

In one exemplary embodiment, the non-active surfaces of the IC processorchips (102) and (103) are rigidly bonded to the cooling device (101)using a silver filled epoxy, filled polymer adhesive, filledthermoplastic or solder, or other thermally conductive bonding materialwith low thermal resistance. To reduce mechanical stresses, the materialof the cooling device (101) is selected to have a TCE (thermalcoefficient of expansion) that closely matches the TCE of the materialof the IC processor chips (102) and (103). The ability to effectivelyuse a rigid bond is limited not only by the difference in the TCEs ofthe materials that form the cooling device (101) and the IC chips, butalso on the temperature range (cycle) in which the semiconductor packagewill operate or be exposed to, as well as size of the area over whichthe rigid bond will be formed.

In one exemplary embodiment, the cooling device (101) comprises amicrochannel cooling device having a plurality of coolant inlet/outlets(101 a) to enable coolant to flow in and out of the cooling device(101). Microchannel cooling devices can be implemented for effectivelycooling electronic devices under conditions of increased heat flux/highpower densities (power/unit area), e.g., ˜800 W/cm². FIGS. 3A and 3B areschematic diagrams that illustrate a microchannel cooling apparatus(300) which can be implemented for the cooling device (101) of FIG. 1.FIG. 3B illustrates a cross-sectional view of FIG. 3A along the line3B-3B. As shown, the exemplary microchannel cooling device (300)comprises a planar substrate (301) (e.g., silicon substrate) that isetched to form a recessed region (302) comprising a plurality ofparallel, microscopic heat conducting fins (303) which define aplurality of channels (304). A second substrate (305) (e.g., siliconsubstrate) (305), or cover plate, is bonded to the etched surface of thesubstrate (301) and the tops of the fins (303) thereby defining achamber for the flow of a coolant (e.g., water) through the channels(304) between the inlets (I) and outlets (O). Heat removal is achievedby thermal contact between the fins (303) and the coolant fluid thatflows through the channels (304).

It is to be understood that the cooling device (300) depicted in FIGS.3A and 3B is merely one exemplary embodiment of the cooling device (101)of FIG. 1, and that any suitable microchannel cooling devices andmethods known to those of ordinary skill in the art may be implementedand customer designed for the intended application. For instance,although the exemplary cooling module (300) is depicted as having twoinlet/outlet ducts, it is to be understood that the number andorientation of the inlet/outlets of the cooling device will varydepending on the particular design. Moreover, the cooling device (300)may be formed to have two separate chambers to allow coolant flowinginside the two chambers in opposite directions.

FIG. 2 is a schematic perspective view of an electronic module accordingto another exemplary embodiment of the invention. FIG. 2 is oneexemplary embodiment of an electronic module (200) which is designedhaving a cooling module disposed between carrier substrates having aplurality of IC chips mounted on the carrier substrates. In particular,FIG. 2 schematically depicts an electronic module (200) comprising acooling device (201) interposed between a first carrier substrate (202)and a second carrier substrate (203) (e.g., silicon substrates). Thecooling device (201) comprises a microchannel cooling device having aplurality of coolant inlet/outlets (201 a) to enable coolant to flow inand out of the cooling device (201). An exemplary embodiment of thecooling device (201) will be discussed below with reference to FIG. 4,for example.

In one exemplary embodiment, the electronic module (200) comprises acomputer “system on a package”, wherein the first carrier substrate(202) comprises an array of IC processor chips (204) and arrays of ICmemory chips (206) and (207) mounted on a surface thereof, and thesecond carrier substrate (203) comprises an array of IC processor chips(205) and arrays of IC memory chips (208) and (209) mounted on a surfacethereof. The high-performance processor chip arrays (204) and (205) aremounted active area down in surface regions of respective carriersubstrates (202) and (203) that are aligned with the cooling module(201). The carrier substrates (202) and (203) comprise one or morelevels of metallization to provide the required conductive lines andinterconnections for signal transmission between the IC memory chips andprocessor chips.

Moreover, in the exemplary embodiment of FIG. 2, the IC memory chip inthe arrays (206)˜(209) are vertically mounted on the respective carriersubstrates (202) and (203) to provide a high density vertical chippackage. In such embodiment, the IC memory chips can be designed suchthat the signal and power connections are formed on the edges of the ICmemory chips that are bonded to the substrates. Methods for verticallymounting IC chips to carrier substrates are known to those of ordinaryskill in the art. For instance, the methods described in U.S. Pat. No.4,266,282, entitled “Vertical Semiconductor Integrated Circuit ChipPackaging”, which is commonly assigned and fully incorporated herein byreference, may be implemented for forming carrier substrates (202) and(203) and vertically mounting the IC memory chips thereto.

The electronic module (200) further comprises separate CIO modules (210)and (211) for corresponding IC processor chip arrays (204) and (205),respectively. The CIO module (210) is connected to the carrier substrate(202) by soldering pins or solder columns (212) and the CIO module (211)is connected to the second carrier substrate (203) by soldering pins orsolder columns (213). Alternatively, the CIO modules (210) and (211) canbe connected to respective carrier substrates (202) and (203) using apin and socket connection, as is well known to those of ordinary skillin the art. The CIO modules (210) and (211) are constructed to includethe required electrical interconnects, bonding pads, integratedcircuits/devices, I/O components, etc., that enable electricalconnection/communication with other electronic components, devices,modules, power sources, etc.

In the exemplary embodiment of FIG. 2, the carrier substrates (202) and(203) provide a thermal path for conducting heat away from the ICprocessor chips and IC memory chips mounted thereon to the coolingdevice (201). In one exemplary embodiment of the invention, the carriersubstrates (202) and (203) are formed having a thickness in a range ofabout 50 microns to about 400 microns. The cooling device (201) isdisposed between the carrier substrates (202) and (203) in alignmentwith surface regions of carrier substrates on which the IC processorchip arrays (204) and (205) are mounted, where the heat density is thegreatest. The high-density IC memory chip arrays (206)˜(208) aredisposed in regions of the respective carrier substrates adjacent thehigh-performance IC processor chip arrays, which extend past the coolingdevice (201). The IC memory chips can be effectively cooled by the heatspreading ability of the carrier substrates and the air columns formedbetween the IC memory chips. The portions of the carrier substrates(202) and (203) which extend past the cooling device (201) are supportedby respective mechanical support structures (214) and (215).

In another exemplary embodiment, the cooling device (201) can be madethe same size as the carrier substrates (202) and (203), in which casethe mechanical support structures (214) and (215) would not be needed.With this exemplary embodiment, since the power dissipation rates aregenerally lower in the memory regions, the cooling channels in thecooling device (201) can be designed accordingly to handle higher powerdensity in the processor region and relatively lower power density inthe memory regions.

In one exemplary embodiment, the carrier substrates (202) and (203) arerigidly bonded to the cooling device (201) using a silver filled epoxy,filled polymer adhesive, filled thermoplastic or solder, or otherthermally conductive bonding material with low thermal resistance. Toreduce mechanical stresses in the thermal interface between the coolingmodule (201) and carrier substrates (202) and (203) due to thermalexpansion/contraction, the material of the cooling device (201) isselected to have a TCE that closely matches the TCE of the material ofthe carrier substrates (202) and (203). Moreover, mechanical stresses inthe thermal interface between the cooling device (201) and the carriersubstrates (202) and (203) are reduced by limiting the size of thecooling device (201) to be aligned with only the high-performance ICprocessor chips. In particular, the cooling device (201) is made smallerthan the carrier substrates (202) and (203) and thus, the surface areaover which the rigid bond (or other thermal interface) between thecooling device and carrier substrates is limited (as compared to formingthe cooling device (201) to have the same planar dimensions as thecarrier substrates).

In another exemplary embodiment of the invention, the cooling device(201) is constructed to have a plurality of conducting through vias thatprovide connection paths between the first and second carrier substrates(202) and (203). In this exemplary embodiment, the surface regions ofthe carrier substrates (202) and (203) that are aligned with the coolingmodule (201) have bonding pads/connectors that can be bonded (via solderballs) to exposed portions of the conducting through vias (or otherinterconnects) on the respective mating surfaces of the cooling module(201) to provide electrical connections between IC chips on thedifferent silicon carriers. Moreover, thermal conduction from the highperformance processor chip arrays (204) and (205) to their respectivesilicon carriers (202) and (203) can be enhanced by filling the emptyspace among the solder ball bonds between the processor chips andsilicon carriers as much as possible with additional solder balls (i.e.thermal via's) and by using a thermally conductive, and electricallyinsulating, underfill material. Additional structures to reduce thethermal conductivity in the silicon carriers and in the chipmetallization levels can be formed, aligned with the additional solderballs, as is known to those of ordinary skill in the art.

It is to be appreciated that in one exemplary embodiment when the ICmemory chips and carrier substrates (202) and (203) are made fromsilicon (or other TCE matched materials) the area density of theindividual solder connections may be increased and/or the height ofsolder connections may be reduced to provide a further reduction inthermal resistance from the IC memory chip arrays (204) and (205) to therespective carrier substrates (202) and (203). Indeed, it isadvantageous to keep the thermal resistance as small as possible toavoid a large delta T, which is the leading factor in chip-to-carrierstress (assuming matched TCEs). This approach is useful withhigh-density micro joins with pitches as low as “1 on “2” mil.

FIG. 4 schematically illustrates one exemplary embodiment of the coolingdevice (201) of FIG. 2, which has electrically conducting vias formedthrough the cooling module to provide electrical signal paths betweensilicon carriers (202) and (203). In particular, FIG. 4 depicts amicrochannel cooling device (400) according to an exemplary embodimentof the invention, which comprises a substrate (401) (e.g., siliconsubstrate) that is etched to form a coolant chamber having microchannelpattern with multiple channel walls (402) and narrow channels (403)formed by the conventional silicon etching technology. A plurality ofconductive through vias (404) are formed inside the channel walls (402).Coolant fluid flows into the microchannel cooling device (400) frominlet ducts (405) and the coolant fluid is diverted to the channels(403) by diverters (406). The coolant is then heated by absorbing heatfrom the channel walls (402) and then flows out of the microchannelcooler device (400) and exits through outlet ducts (407). The arrowsdenote the coolant flow direction. There are periodic widening portionsalong the channel walls (402) where the through vias (404) are located.Advantageously, the through vias (404) not only provide shortcommunication paths for signal transmissions between the carriersubstrates, but enable enhanced cooling of the module (200) due to theclose proximity of the conductive through vias with the cooling fluidthat flows through the microchannels (403).

FIG. 5 is a schematic cross-sectional view of an electronic moduleaccording to another exemplary embodiment of the invention. Morespecifically, FIG. 5 schematically illustrates an electronic module(500) for integrating a microchannel cooler with IC chips mounted facedown on a high-density wiring carrier such as a silicon carrier. Inparticular, the exemplary package comprises a first level packagecarrier (501) (e.g., ceramic substrate) with an array of large (˜1 mmpitch) solder balls (B₁) (e.g., BGA, ball grid array) that are used forbonding the substrate (501) to a card or printed circuit board (notshown). The module (500) further comprises an intermediate (or 2^(nd)level) carrier substrate (502) (e.g., silicon substrate) having aplurality of IC chips (503) and (504) that are flip-chip bonded thereto.The intermediate carrier substrate (502) is bonded to the first levelcarrier substrate (501) via an array of fine pitch (˜0.2 mm pitch)solder balls (B₂), such as C4's.

The carrier substrate (502) is constructed to comprise high densitywiring on the top surface thereof for providing electricalinterconnections to the IC chips (503) and (504) via high-density solderbump arrays (B₃) and (B₄) (˜0.05 mm pitch), respectively. Moreover, theintermediate carrier substrate (502) comprises a plurality of conductivevias that are formed through the carrier substrate (502) to enableelectrical connections with the first level package substrate (501) viathe solder bump array (B₂). The intermediate carrier substrate (502) andceramic substrate (501) are designed to provide a space transformationbetween electrical connections between the fine pitch solder ball arrays(B₃ and B₄) and the printed circuit board bond ball array (B₁) and tointerconnect multiple chips on the intermediate carrier substrate (502).

The electronic module (500) further comprises an integrated microchannelcooling device (505) that is thermally bonded to the non-active surfacesof the IC chips (503) and (504) via respective rigid thermal bonds (B₅)and (B₆). The bonding material used for the rigid thermal bonds (B₅) and(B₆) may comprise any suitable material with low thermal resistivity,such as a solder, metal layer, Ag epoxy, or a filled polymer, to therebyallow sufficient heat conduction from the chips to the microchannelplate (506). A low thermal resistance bond such as a metal joint, solderjoint, or a filled thermal adhesive such as a Ag epoxy, or other joiningmeans could be used, as long as the bonding thickness is sufficientlythin and compatible with the cooling requirements. Further, it isdesirable that the bonds (B₅) and (B₆) are reworkable, so that themicrochannel cooler (505) can be removed from the chips, when necessary,to either replace the microchannel cooler device (505) or replace one ormore of the chips (503) and (504).

In one exemplary embodiment, the microchannel cooler module (505)comprises a microchannel plate (506) connected to a manifold plate (507)via bond (B₇). The microchannel cooling device (505) extends over the ICchips and is approximately the same size, or slightly larger than, theintermediate carrier substrate (502). The microchannel and manifoldplates (506) and (507) may be formed from silicon substrates, or othermaterials having TCE that matches the TCE of the material forming the ICchips (503) and (504). The microchannel plate (506) comprises aplurality of microfins (506 a) that define channels (506 b), which areformed in surface regions of the microchannel plate (506) that arealigned with the IC chips (503) and (504). Further, the manifold plate(507) (or manifold cover), which is bonded to the microchannel plate(506), comprises a plurality of fluid manifolds formed therein, whereineach fluid manifold comprises a corresponding manifold channel (507 b)formed in one surface the manifold plate (507) and a correspondingpattern/series of fluid vias (507 a) that form openings which extendfrom the opposing surface of the manifold plate (507) to various pointsalong the corresponding manifold channel (507 b).

The microchannel and manifold plates (506) and (507) may be formed usingthe methods described in U.S. patent application Ser. No. 10/883,392,filed Jul. 1, 2004, entitled “Apparatus and Methods for MicrochannelCooling of Semiconductor Integrated Circuit Packages”, which is commonlyassigned and fully incorporated herein by reference. In general, thisapplication describes methods for constructing integrated microchannelcooler devices that include supply/return manifolds andmicrochannels/microfins which are structured, patterned, dimensionedand/or arranged in a manner that minimizes pressure drop and increasesuniformity of fluid flow and distribution along coolant flow paths, aswell as maintain the structural integrity of the manifold plate toprevent breakage during manufacturing. For instance, as explained indetail in U.S. Ser. No. 10/883,392, the manifold plate (507) is designedsuch that the inlets/outlets (507 a) for a given manifold channel (507b) are formed as a series of circular openings, or openings with roundedcorners, arranged in a zig-zag pattern, to reduce wafer cracking duringmanufacturing. The manifold channel (507 b) comprises tapered channelsegments formed between the circular openings on the plate surface thatfaces the microchannels. The manifold is designed to reduce thepotential of wafer breakage by using circular openings to minimizestress concentrations which can serve as crack nucleation sites,minimizing the total cavity area of the channel manifolds by usingrecessed regions of the microchannel pattern to act as a manifold inconjunction with the manifold channels, and avoid aligning the cavitiesalong the (100) Si cleavage planes. In another exemplary embodiment ofthe invention, an integrated microchannel cooler device (505) may beformed from a single plate that is constructed with both microchannelsand supply/return manifolds structures using the methods described inthe above incorporated application.

The microchannel plate (506) and manifold plate (507) are bonded usingbonding material (B₇) that is sufficient to provide a watertight seal,but the bond (B₇) does not have to provide a low thermal resistance.Accordingly, bonding methods such as direct wafer bonding, fusionbonding, anodic bonding, glass frit bonding, solder bonding, polymeradhesive bonding, or any other suitable bonding method may be used tojoin the microchannel and manifold plates (506) and (507).

The electronic module (500) further comprises a gasket (508) and packagecap (509). The package cap (509) comprises fluid inlet/outlet manifolds(509 a) that are aligned to corresponding inlets/outlets (507 a) of themicrochannel cooler device (505). The package cap (509) is connected tothe back surface of the microchannel cooler (505) via the gasket (508).In one exemplary embodiment, the gasket (508) is adhered to both themicrochannel cooler (505) and the package cap (509) using a hightemperature epoxy or other suitable adhesive. In the exemplaryembodiment of FIG. 5, the package cap (509) is designed as a fluiddistribution manifold for delivering coolant fluid to/from integratedmicrochannel cooler device (505). The manifold structure of the packagecap (509) can be designed using methods described in the aboveincorporated patent application U.S. Ser. No. 10/883,392.

For instance, the fluid distribution manifolds (509 a) can be designedin a manner to minimize overall system pressure drop by using variablecross-sectional fluid supply/return channels for delivering coolantfluid to/from integrated microchannel cooler devices. Moreover, with theexemplary microchannel cooling device (505) depicted in FIG. 5, thefluid vias (507 a) are formed on the back surface of the manifold plate(507) chip to input/output coolant fluid to/from the integratedmicrochannel cooler device, which enables the microchannel cooler device(505) to be dimensioned such that is does not extend significantlybeyond the area of the array of chips to be cooled.

FIG. 6 is a schematic cross-sectional view of an electronic module (600)according to another exemplary embodiment of the invention. Inparticular, the electronic module (600) is an alternate embodimentsimilar to the electronic module (500) of FIG. 5, but wherein ahigh-performance processor chip (601) and memory chips (602) and (603),which have different thicknesses, are flip-chip mounted on anintermediate carrier substrate (604). In the exemplary embodiment ofFIG. 6, the processor chip (601), which has a higher power density thanthe memory chips (602) and (603), is mounted in a center region of theintermediate carrier substrate (604), and the lower power density memorychips (or other chips), are mounted along the peripheral regions of thecarrier (604). The chips (601), (602) and (603) are rigidly bonded amicrochannel cooler device (605) via rigid thermal bonds B1, B2 and B3,respectively.

With the higher power-density chip (601), it is desirable to have alower total thermal resistance in the thermal bond (b1) between the chip(601) and the microchannel cooler device (605) to maintain the samemaximum junction temperature as compared to the lower power densitychips (602) and (603). In particular, when assembling a microchannelcooler (605) over multiple chips (601˜603) on a carrier (604) asdepicted in the exemplary embodiment of FIG. 6, it is desirable toinsure that the high power chip (601) have the thinnest bond layer ofthermally conductive material to attach the chip (601) to themicrochannel cooler (605). For example, in FIG. 6, if both memory chips(602) and (603) were thicker than the processor chip (601), thethickness of the bond line of the thermally conductive material (B₁)used to attach the processor chip (601) to the microchannel cooler (605)would be greater than that of the bonds B₂ and B₃. Thus, in theexemplary embodiment of FIG. 6, the lower power-density memory chips(602) and (603) are thinned slightly as compared to the high powerprocessor chip (601) to insure that the thickness of the bond line isdetermined by the back surface of the processor chip (601). Methods forthinning of a lower power chip to accommodate different power densitieswhile maintaining a simple hat or lid structure are described in U.S.patent application Ser. No. 10/711,023, filed on Aug. 18, 2004, entitled“Multiple Power Density Chip Structure”, which is commonly assigned andfully incorporated herein by reference. The power density of the chipsand also the desired junction temperature or power distribution of poweron the chip are factors that are considered when determining the thermalresistance required to adequately cool the chips. Various methods forassembling an electronic module having structures similar to thosedepicted in the exemplary embodiment of FIGS. 5 and 6 will now bedescribed. An exemplary assembly process begins with mounting an arrayof chips to an intermediate silicon carrier using any suitable flip-chipbonding method known to those of ordinary skill in the art. Optionally,the mounted chips may be under filled and/or the back surface of thechips may be planarized by polishing, lapping, or grinding. Then, apreviously assembled and pressure tested silicon microchannel coolerdevice can be attached to the back surface of the chips mounted on thecarrier using a solder, metal layer, Ag epoxy, filled polymer, or otherrigid thermally conductive bonding method. The silicon carrier, chips,and microchannel cooler package can then be assembled to a first levelpackage using C4's. In a final step, a package cap with correspondingdesigned fluid inlet/outlet manifolds, is connected to the back surfaceof the microchannel cooler using a gasket. The gasket maybe adhered toboth the microchannel cooler and the cap using a high temperature epoxyor other suitable adhesive. In an alternate embodiment, the microchannelcooler can be attached to the chips and silicon carrier after they areassembled to the first level package using C4's.

As discussed above, the use of a silicon carrier has a number ofsignificant advantages such as using finer pitch electrical connectionsto the chips to provide greater electrical signaling capacity andgreater wiring capacity. However, silicon carriers are difficult to coolusing conventional methods because of their limited thickness and largearea. A typical silicon carrier is between about 50 microns and about200 microns thick (and could be as thick as 500 microns), but thelateral size could be 4 or 5 cm along each edge.

The exemplary package structures of FIGS. 5 and 6 according to theinvention, which integrate silicon carriers and microchannel coolers,afford a number of significant advantages including, for example,providing a low thermal resistance path to the integrated microchannelcooler and using the microchannel cooler as a means of providingadditional mechanical strength to thin silicon carriers to preventfracture during subsequent processing and operation.

Although exemplary embodiments have been described herein with referenceto the accompanying drawings, it is to be understood that the presentsystem and method is not limited to those precise embodiments, and thatvarious other changes and modifications may be affected therein by oneskilled in the art without departing from the scope or spirit of theinvention. All such changes and modifications are intended to beincluded within the scope of the invention as defined by the appendedclaims.

1. An electronic module, comprising: a first carrier substrate; a secondcarrier substrate formed of silicon, which is bonded to the firstcarrier substrate; a plurality of IC (integrated circuit) chipsflip-chip bonded to the second carrier substrate; a microchannel coolingdevice formed of silicon, the microchannel cooling device comprising afirst surface that is thermally bonded to a non active surface of eachof the IC chips, the microchannel cooling device having a plurality ofcoolant inlet and outlet manifolds formed in a second surface oppositethe first surface; a package cap attached to the second surface of themicrochannel cooling device using a flexible seal, the package capcomprising fluid distribution manifolds that are aligned tocorresponding inlet and outlet manifolds of the microchannel coolingdevice.
 2. The electronic module of claim 1, wherein the first carriersubstrate comprises a ceramic package substrate.
 3. The electronicmodule of claim 1, wherein the second carrier substrate has a thicknessof less than about 0.5 mm, and wherein the second carrier substratecomprises electrical through vias.
 4. The electronic module of claim 1,wherein the second carrier substrate has a thickness in a range of about50 microns to about 200 microns, and wherein the second carriersubstrate comprises electrical through vias.
 5. The electronic module ofclaim 1, wherein a pitch of the electrical interconnections between thesecond carrier substrate and the IC chips is less than or equal to about300 microns and more preferably less than about 100 microns.
 6. Theelectronic module of claim 1, wherein the first surface of themicrochannel cooling device is thermally bonded to the non-activesurface of each of the IC chips using rigid bonding material.
 7. Theelectronic module of claim 6, wherein the rigid bonding materialcomprises solder, metal, silver filled epoxy, or a filled polymermaterial.
 8. The electronic module of claim 1, wherein the non-activesurface of one or more of the IC chips mounted on the second carriersubstrate is planarized prior to being bonded to the microchannelcooling device.
 9. The electronic module of claim 7, wherein a thicknessof rigid bonding material between the non-active surface of the chipsand the first surface of the microchannel cooling device is varied fordifferent chips in accordance with a thermal resistance required for theIC chips.